Field of the Invention
The present invention relates to, for example, a measuring apparatus for measuring an optical characteristic of a sample.
Description of the Related Art
Conventionally, for the purpose of evaluating the appearances of print materials, coated surfaces, and products, for example, standards for evaluating the optical characteristic of samples (their surfaces, their interiors, and so on) are being defined by JIS and ISO. For example, ISO 2813 and JIS Z 8741 define the specular gloss. ASTM E430 defines the haze and the distinctness of image (DOI). In addition, JIS K 7374 and ASTM D5767 define the image clarity. Furthermore, a unique index for evaluating the glossiness is also being proposed. Measuring apparatuses that obtain such a diffusion characteristic or an optical characteristic of samples are known. Such measuring apparatuses include an apparatus configured in accordance with a specific standard. Meanwhile, such measuring apparatuses include an apparatus that first obtains the diffusion characteristic (e.g., a bidirectional reflectance distribution function (abbreviated as BRDF)). This apparatus may function as a general-purpose apparatus that obtains a plurality of additional indices (e.g., the specular gloss, the haze, and the image clarity) on the basis of the diffusion characteristic. In an optical system in such a general-purpose measuring apparatus, a sample may be disposed in the pupil, a secondary light source may be provided at the anterior focal point, and an image sensor may be provided at the posterior focal point.
Japanese Patent Laid-Open No. 2010-276492 discloses an apparatus in which a pinhole serves as a secondary light source and an image of the pinhole is taken by an image sensor. Since the pinhole serves as the secondary light source, the diffusion characteristic with a high angular resolution can be obtained, but this apparatus may suffer from a disadvantage in securing the quantity of light or the luminous sensitivity. Meanwhile, Japanese Patent Laid-Open No. 2008-256454 discloses an apparatus in which an aperture in an aperture plate serves as a secondary light source and an image of the aperture is taken by an image sensor.
Increasing the angle of the aperture in the aperture plate provides an advantage in securing the quantity of light but suffers from a disadvantage in the angular resolution of the obtained optical characteristic, such as the diffusion characteristic.